Defined but not used is not detected for data types with instances

module Unused () where

data U = U deriving Show

does not report

Unused.hs:3:6: Warning:
    Defined but not used: type constructor or class `U'

Unused.hs:3:10: Warning: Defined but not used: data constructor `U'

This message is only displayed without "deriving". I know, instances are always exported, but these instances cannot be used.

Considering that all types may get Typeable instances, no unused warning would ever be issued for data types.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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